Pressure and/or flow compensating means

ABSTRACT

The control circuit of a high pressure work system powered by a variable displacement-positive displacement pump is provided with a compensating valve for controlling the pump displacement. The compensating valve is responsive to pressure in a control circuit and in the work circuit as well as to fluid flow in another circuit to alter the displacement of the work system pump.

United States Patent 11 1 Haak et al.

1 1 Jan. 30, 1973 PRESSURE AND/OR FLOW COMPENSATING MEANS Williard J. llaak, Peoria; Howard A. Marsden, Pekin, bothof ll].

Caterpillar Tractor Co., Peoria, [IL April-26, 1971 Inventors:

Assignee:

Filed:

Appl. No.:

U.S. c1 60/52 vs, 60/52 HE Int. Cl ..Fl5b 15/18 Field of Search ..60/52 VS, 52 HE, 52 SR [56] References Cited UNITED STATES PATENTS 2,238,061 4/1941 Kendrick ..60/52 VS 3,477,225 11/1969 Cryder et al ..60/52 vs Primary Examiner-Edgar W. Geoghegan Attorney-Fryer,'Tjensvold, Feix, Phillips & Lempio 57 ABSTRACT The control circuit of a high pressure work system powered by a variable displacement-positive displacement pumpis provided with a compensating valve for controlling the pump displacement. The compensating valve is responsive to pressure in a control circuit and in the work circuit as well as to fluid flow in another circuit to alter the displacement of the work system pump;

4 Claims, 2 Drawing Figures IENGWE PATENTEDJAN 30 I973 ENGINE INVENTORS I WILLARD J. HAAK HOWARD A. MARSDEN o y I A'm'omms PRESSURE AND/OR FLOW COMPENSATING MEANS BACKGROUND OF THE INVENTION Hydraulic power systems are extensively employed 0 in lifting, loading, and other handling systems. Such hydraulic systems are provided with a prime mover, such as a gasoline or diesel engine driving a pump for delivery of pressurized fluid to the system. The hydraulic system is generally capable of delivering substantially the full horsepower of the prime mover to the work output of the system. One difflculty with such systems is that when engine speed is less than that for full horsepower, the hydraulic work system is still capable of demanding full maximum engine horsepower. This condition generally stalls the engine or at least hinders engine response considerably.

SUMMARY or THE INVENTION BRIEF DESCRIPTION OF TI -IE DRAWINGS The above and other objects and advantages of the present invention will become apparent from the following description when read in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic illustration of a typical hydraulic power work output system embodying the present invention;

FIG. 2 is a side elevational view in section of a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings, and in particular to FIG. 1, there is illustrated a schematic illustration of a hydraulic power system in combination with a low pressure hydraulic control system embodying the present invention. The highpressure work output system comprises a supply pump 12 for supplying fluid to-a high pressure variable displacement pump 14 which is driven by a suitable prime mover 15 which may be, for example, a diesel or gasoline powered engine. High pressure fluid from the variable displacement pump 14 is supplied by means of a conduit 16 to a directional control valve 18 which controls the direction of power output from the work system such as by means of a double-acting hydraulic motor 20.

A low'pressure hydraulic control circuit for controlling the valve 18 comprises a fixed displacement pump 22 directly drives by engine 15 and having a flow output which is directly proportional to vehicle engine speed. Fluid from the pump 22 is delivered by a conduit 24, a venturi 50 and a conduit 4810 an accumulator charging valve 26, thence to a pilot control valve 30 which controls the directional control valve 18. The pilot control valve 30 is generally manually controlled and supplies fluid by'means of conduits 32 and 34 to the valve 18.

A conduit 36 supplies fluid to a servo valve 38 which controls a fluid motor 40 for varying the displacement of pump 14. A conduit 42 carries control fluid, from pilot control valve 30 to another input side to servo valve 38 and control fluid pressure is-communicated via conduit 44, to a compensating valve 46 which will be described in detail below. I

The flow of fluid in conduit 48 is monitored by means of venturi 50, with conduits 52 and 54 supplying a differential pressure signal created across the venturi to the compensating valve 46. I

Referring now to FIG. 2, there is illustrated a compensating valve 46 which comprises a valve member 58 which acts as a variable setting relief valve, mounted for reciprocal movement within a substantially cylindrical chamber 60. The valve member 58 is biased to the closed position by means of aspring 62 and thereby functions to cut off or block a flow of fluid from conduit 44' to an exhaust line 64 leading back to the reservoir. Face 66 of valve member 58 functions as a piston in response to pressurized fluid from conduit 44. A second piston 68 is reciprocally mounted in a chamber 70 and cooperatively engages valve member 58 for urg-' ingthe valve to the opened position in response to into one end of the chamber 76 to relieve pressure or force against spring 62. Conduits 52 and 54 provide communication with chamber 76 on opposite sides of the piston 74.

In order to understand the operation of the present invention, it is essential to understand the operation of a high pressure work system in which the present invention would be employed. Typically, such systems employ a variable stroke positive displacement pumpsuch as 14 driven. by the vehicle engine 15 which supplies pressurized fluidto a work' output member such as a cylinder 20. The horsepower output from the system will be a function of the load on the work cylinder 20 and the rate of movement of the output member from that cylinder. The rate of movement of the cylinder will be a function of the flow rate in the system which will be determined by the stroke of the pump 14 and its rpm. The pressure of the system will be normally the pressure required to move the output from the cylinder 20 against the workload. Thus, it can be seen that if the stroke of the pump 14 is at its maximum for a given r.p.m. setting of the prime mover, the flow rate through the circuit will be large and if a load is extremely large, then there will be a high demand of torque from the prime mover.

If the load on the system exceeds that which the engine can deliver at the given stroke, the engine will stall. The present invention eliminates this problem by the compensating valve 46 which senses the system pressure through line or conduit 56 and pilot signal pressure through the line 44. These pressures as they increase tend to move valve element 58 to the left and thereby relieve pressurein line 44 which controls servo valve 38 which in turn controls the fluid valve motor 40 for altering the displacement of pump 14.

The'r.p'.rn. of the engine which is also related to the horsepower output of the engine is compensated for by means of a flow sensing means which comprises a venturi 50 which senses the flow rate in a portion of a controlcircuit. Thisportionj of the control circuit has a flow rate which is directly proportional to the prime mover speed since the fluid is'supplied by means of a positive displacement'pump 22 directly driven by the prime mover. When engine speed is high (rated), flow through the venturi is high and the differential pressure signal generated by the venturi is high. Piston 74 will be held to the right against spring 78 and the force on piston 58 imposed by spring 62 will be at a maximum. As a result, the pressure that can be developed in line 44 will be at a maximum and it will be possible to obtain maximum displacement (therefore, maximum flow) of pump 14.

Q As engine speed decreases, flow rate and pressure differential across the venturi decrease tending to move the piston 74 to the left. This decreases the force that spring 62 imposes on valve 58 and decreases the maximum pressure level that can be obtained in line 44. Since the pressure level inline 44 is directly proportional to displacement of pump l4,limiting the maximum pressure in line 44 also limits the maximum displacement of pump 14. Therefore, as engine speed and horsepower decrease, flow compensation of the system takes place automatically.

What is claimed is:

1. In combination a low pressure control" circuit operatively connected for controlling a high pressure work output system, said work system including -a high pressure-variable displacement pump, said control circuit including a fixed displacement pump, prime mover means operatively connected to drive said pumps; a

selectively actuable control valve in said control circuit, means operatively connecting the control valve to,

control said variable displacement pump whereby the amount of flow in the work output system is initiallydetermined by said control valve and is controlled by varying the displacement of said variable displacement pump, and compensating valve means in said control circuit and responsive to a flow rate established by said fixed displacement pump in said control circuit and to fluid pressure in said pressure work system established by said variabledisplacement pump to control the output of said variable displacement pump.

2; Inv a low pressure control circuit for controlling a high pressure work output system, a selectively actuable control valve in said circuit, means connecting the control valve to a variable displacement pump whereby valve member and responsive to pressure in said work output system to urge said valve member to an o riposition; and, secon pis on means operatively associated with said valve memberand responsive to the rate of fluid flow in said control circuit to urge said valve member to the closed position.

3. In a low pressure control circuit for controlling a high pressure work output system, a selectively actuable control valve in said circuit, means connecting the control valve to a variable displacement pump whereby the amount of flow in the work output system is controlled, and compensating valve means responsive to a flow rate in said control circuit and to fluid pressure in said pressure work system to control the output, of said pump, said compensating valve means comprising:

a cylindrical relief valve element confined in a cylindrical bore; Y Y

' biasing means for differentially biasing said valve element to-a closed position in response to-a rate of flow of fluid in one portion of said circuit;

a firstpiston means responsive to fluid in one portion of said circuit to open said valve; and,

a second piston means responsive to fluid in a second portion of said circuit to assist the fluid in said one portion of said circuit to open said valve.

4. The valve of claim 3 comprising: i

a third piston means;

said three piston means are arranged in'separate concentricbores;

. one of said piston means'functions as a valve element; Y 1 1 spring means interposed between two of said piston means; 7

one of said piston means being responsive to rate of flow of fluid in said circuitto bias said valve piston;

another of said pistons being responsive to pressure in a portion of said circuit to bias said valve piston.

* I III i 

1. In combination a low pressure control circuit operatively connected for controlling a high pressure work output system, said work system including a high pressure variable displacement pump, said control circuit including a fixed displacement pump, prime mover means operatively connected to drive said pumps; a selectively actuable control valve in said control circuit, means operatively connecting the control valve to control said variable displacement pump whereby the amount of flow in the work output system is initially determined by said control valve and is controlled by varying the displacement of said variable displacement pump, and compensating valve means in said control circuit and responsive to a flow rate established by said fixed displacement pump in said control circuit and to fluid pressure in said pressure work system established by said variable displacement pump to control the output of said variable displacement pump.
 1. In combination a low pressure control circuit operatively connected for controlling a high pressure work output system, said work system including a high pressure variable displacement pump, said control circuit including a fixed displacement pump, prime mover means operatively connected to drive said pumps; a selectively actuable control valve in said control circuit, means operatively connecting the control valve to control said variable displacement pump whereby the amount of flow in the work output system is initially determined by said control valve and is controlled by varying the displacement of said variable displacement pump, and compensating valve means in said control circuit and responsive to a flow rate established by said fixed displacement pump in said control circuit and to fluid pressure in said pressure work system established by said variable displacement pump to control the output of said variable displacement pump.
 2. In a low pressure control circuit for controlling a high pressure work output system, a selectively actuable control valve in said circuit, means connecting the control valve to a variable displacement pump whereby the amount of flow in the work output system is controlled, and compensating valve means responsive to a flow rate in said control circuit and to fluid pressure in said pressure work system to control the output of said pump, said compensating valve means comprising: a valve member normally biased to a closed position; first piston means operatively associated with said valve member and responsive to pressure in said work output system to urge said valve member to an open position; and, second piston means operatively associated with said valve member and responsive to the rate of fluid flow in said control circuit to urge said valve member to the closed position.
 3. In a low pressure control circuit for controlling a high pressure work output system, a selectively actuable control valve in said circuit, means connecting the control valve to a variable displacement pump whereby the amount of flow in the work output system is controlled, and compensating valve means responsive to a flow rate in said control circuit and to fluid pressure in said pressure work system to control the output of said pump, said compensating valve means comprising: a cylindrical relief valve element confined in a cylindrical bore; biasing means for differentially biasing said valve element to a closed position in response to a rate of flow of fluid in one portion of said circuit; a first piston means responsive to fluid in one portion of said circuit to open said valve; and, a second piston means responsive to fluid in a second portion of said circuit to assist the fluid in said one portion of said circuit to open said valve. 